I left my Fitbit charging overnight and the battery drained and now it won't charge

SOURCE: My battery drains overnight

Check and make sure the Air Condition cluch is disengageing, I had the same problem afew years back.

SOURCE: left key in ignition overnight, now car wont start

try checking the main relay under the dash

SOURCE: draw on battery when car on

First disconnect the battery overnight just to make sure the battery is not self discharging......if it's dead or down in charge while disconnected....time for a new one.
Now.....if the battery is good....disconnect one battery cable and place a 12 volt test light between the cable and the battery post the cable had just been attached to. A bright light means a drain in the car.
Your job is to remove one fuse at a time until the light dims.
A dim light is OK...clock memory etc.
Remember....a open car door is a drain......the dome light.....so keep them closed while pulling fuses.
Also....if the fuses don't show a drain......disconnect ALL wires from the alternator....there could be a drain there.
Just keep disconnecting one thing at a time until the light goes out or dims.

SOURCE: New Battery + Possible Parasitic Drain + Weird Problems

Many new batteries will come with bad cells from the factory. If you just purchased this, I would definately try returning it asap. As soon as you get the new one, immediately hook it up to the charger to see if you have the same results. I have heard of others who have gone through two bad (new) batteries before getting a good one.

SOURCE: tHE BATTERY IS DRAINING OVERNIGHT. ALTERNATOR IS

If the battery is draining at all ,beyond 40 milli amps continuous,which is what keeps the radio clock,pcm (computer) and other devices powered up,then something is not timing out,such as windows,door locks,on the LS the radio etc. Retained memory is just that or it goes to sleep ie no current flow. I won't go into how you check current flow but it is fairly easy. The time consuming task will be to find the offender. You could pull all the fuses and replace them one at a time,but need an ampere meter in the circuit,so that's why I won't go into it. Now fuses alone are just a start and time here is limited. The LS has an awfull lot of stuff. I have a 2004. Even the Alt and a long list of things could cause this.